TRUNCATE表后对表大小进行查询，表的空间没有释放完毕？
对此进行实验测试，结果如下：(测试环境LINUX+ORACLE11.2.0.3)
创建表时语句指定了storage (MINEXTENTS 5);时，TRUNCATE后还有5个EXTENT；
创建表时语句不指定storage (MINEXTENTS参数，即使用默认值时；TRUNCATE后只有1个EXTENT；
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实验1：指定了storage (MINEXTENTS 5)
SQL> create tablespace test2 datafile '/u01/oracle/base/oracle/oradata/bys7/test2.dbf' size 10m uniform size 40k;
Tablespace created.
SQL> show user
USER is "TEST"
SQL> create table test1(aa number,name varchar2(128)) tablespace test2 storage (MINEXTENTS 5);
Table created.
SQL> select owner,SEGMENT_NAME,TABLESPACE_NAME,EXTENT_ID from dba_extents where SEGMENT_NAME='TEST1';
OWNER SEGMENT_NAME TABLESPACE_NAME EXTENT_ID
------------------------------ ------------ --------------- ----------
TEST TEST1 TEST2 0
TEST TEST1 TEST2 1
TEST TEST1 TEST2 2
TEST TEST1 TEST2 3
TEST TEST1 TEST2 4
SQL> insert into test1 select object_id,object_name from dba_objects;
13723 rows created.
SQL> commit;
Commit complete.
SQL> select owner,SEGMENT_NAME,TABLESPACE_NAME,EXTENT_ID from dba_extents where SEGMENT_NAME='TEST1';
OWNER SEGMENT_NAME TABLESPACE_NAME EXTENT_ID
------------------------------ ------------ --------------- ----------
TEST TEST1 TEST2 0
TEST TEST1 TEST2 1
TEST TEST1 TEST2 2
TEST TEST1 TEST2 3
TEST TEST1 TEST2 4
TEST TEST1 TEST2 5
TEST TEST1 TEST2 6
TEST TEST1 TEST2 7
TEST TEST1 TEST2 8
TEST TEST1 TEST2 9
TEST TEST1 TEST2 10
TEST TEST1 TEST2 11
12 rows selected.
SQL>truncate table test1;
Table truncated.
SQL> select owner,SEGMENT_NAME,TABLESPACE_NAME,EXTENT_ID from dba_extents where SEGMENT_NAME='TEST1';
OWNER SEGMENT_NAME TABLESPACE_NAME EXTENT_ID
------------------------------ ------------ --------------- ----------
TEST TEST1 TEST2 0
TEST TEST1 TEST2 1
TEST TEST1 TEST2 2
TEST TEST1 TEST2 3
TEST TEST1 TEST2 4
SQL> select SEGMENT_NAME,TABLESPACE_NAME,BYTES/1024 kb,EXTENTS,BLOCKS,INITIAL_EXTENT,NEXT_EXTENT,MIN_EXTENTS,MAX_EXTENTS from dba_segments where SEGMENT_NAME='TEST1';
SEGMENT_NAME TABLESPACE_NAME KB EXTENTS BLOCKS INITIAL_EXTENT NEXT_EXTENT MIN_EXTENTS MAX_EXTENTS
------------ --------------- ---------- ---------- ---------- -------------- ----------- ----------- -----------
TEST1 TEST2 200 5 25 204800 40960 1 2147483645
实验2：创建表时不指定storage (MINEXTENTS参数 使用默认值
SQL> create table test2 tablespace test2 as select object_id,object_name from dba_objects;
Table created.
SQL> set pagesize 1000
SQL> select owner,SEGMENT_NAME,TABLESPACE_NAME,EXTENT_ID from dba_extents where SEGMENT_NAME='TEST2';
OWNER SEGMENT_NAME TABLESPACE_NAME EXTENT_ID
------------------------------ ------------ --------------- ----------
TEST TEST2 TEST2 0
TEST TEST2 TEST2 1
TEST TEST2 TEST2 2
TEST TEST2 TEST2 3
TEST TEST2 TEST2 4
TEST TEST2 TEST2 5
TEST TEST2 TEST2 6
TEST TEST2 TEST2 7
TEST TEST2 TEST2 8
TEST TEST2 TEST2 9
TEST TEST2 TEST2 10
TEST TEST2 TEST2 11
12 rows selected.
SQL> truncate table test2;
Table truncated.
SQL> select owner,SEGMENT_NAME,TABLESPACE_NAME,EXTENT_ID from dba_extents where SEGMENT_NAME='TEST2';
OWNER SEGMENT_NAME TABLESPACE_NAME EXTENT_ID
------------------------------ ------------ --------------- ----------
TEST TEST2 TEST2 0
